In a semiconductor device such as a field effect transistor, an isolating surface protection film, that is, a so-called surface passivation film, having through-holes is formed on a semiconductor layer, and then, electrodes are formed in the through-holes. In such a semiconductor device, the electrodes are formed at high temperatures in order to provide an excellent electrical connection between each electrode and the semiconductor layer. Here, when the surface passivation film and the electrodes are in contact with each other, the electrode material may diffuse into the surface passivation film during the preparation of the electrodes. The region of the surface passivation film into which the electrode material diffuses becomes conductive and brings about a possibility to cause a decrease in a breakdown voltage, an increase in current collapse, and variations in characteristics of each device.